Pesq. Vet. Bras. 35(6):583-589, junho 2015 DOI: 10.1590/S0100-736X2015000600017 Macroscopic description of the external and middle ear of paca (Cuniculus paca Linnaeus, 1766)1 Leandro L. Martins2*, Ijanete Almeida-Silva3, Maria Rossato3, Adriana A.B. Murashima3, Miguel A. Hyppolito3 and Marcia R.F. Machado4 ABSTRACT.- Martins L.L., Almeida-Silva I., Rossato M., Murashima A.A.B., Hyppolito M.A. & Machado M.R.F. 2015. Macroscopic description of the external and middle ear of paca (Cuniculus paca Linnaeus, 1766). Pesquisa Veterinária Brasileira 35(6):583-589. Depar- tamento de Anatomia Animal, Escola de Veterinária, Universidade de Ingá, Rodovia PR-317 nº 6114, Maringá, PR 87035-510, Brazil. E-mail: [email protected] Paca (Cuniculus paca), one of the largest rodents of the Brazilian fauna, has inherent characteristics of its species which can conribute as a new option for animal experiman- tation. As there is a growing demand for suitable experimental models in audiologic and otologic surgical research, the gross anatomy and ultrastructural ear of this rodent have been analyzed and described in detail. Fifteen adult pacas from the Wild Animals Sector herd of Faculdade de Ciências Agrárias e Veterinárias, Unesp-Jaboticabal, were used in this study. After anesthesia and euthanasia, we evaluated the entire composition of the exter- nal ear, registering and ddescribing the details; the temporal region was often dissected for a better view and detailing of the tympanic bulla which was removed and opened to expose the ear structures analyzed mascroscopically and ultrastructurally. The ear pinna has a triangular and concave shape with irregular ridges and sharp apex. The external au- ditory canal is winding in its path to the tympanic mebrane. The tympanic bulla is is on and membranous structures bounded by the tympanic membrane and the oval and round the back-bottom of the skull. The middle ear is formed by a cavity region filled with bone ear is similar to the guinea pig and from the viewpoint of experimental model has major advantageswindows. The compared tympanic with membrane the mouse is flatear. and seals the ear canal. The anatomy of the paca INDEX TERMS: Ear, paca, Cuniculus paca, rodent, temporal bone, ultrastructure. RESUMO.- [Descrição macroscópica da orelha externa e por modelos experimentais apropriados para pesquisas media da paca (Cuniculus paca Linnaeus, 1766).] A paca audiológicas e otológica cirúrgicas foram analisados e des- (Cuniculus paca), um dos maiores roedores da fauna bra- critos em detalhes a anatomia macroscópica e ultraestrutu- sileira, possui características inerentes à sua espécie que ral da orelha desse roedor. Para o estudo, utilizaram-se 15 podem contribuir como uma nova opção de animal expe- animais adultos provenientes do plantel do Setor de Ani- rimental; assim, considerando-se que há crescente busca mais Silvestres da Faculdade de Ciências Agrárias e Vete- rinárias, Unesp-Jaboticabal, Jaboticabal/SP. Após anestesia 1 Received on April 2, 2014. e eutanásia, avaliou-se toda a composição da orelha exter- Accepted for publication on March 8, 2015. na, registrando-se e descrevendo-se os detalhes, também 2 Departamento de Medicina veterinária, Universidade Estadual de Maringá, se dissecou a região temporal para melhor visibilização e Campus de Umuarama, Estrada da Paca s/n, Bairro São Cristóvão, Umuarama, detalhamento da bula timpânica e estas foram removidas e PR 87507-190, Brasil. *Corresponding author: [email protected] - 3 Departamento de Oftalmologia, Otorrinolaringologia e Cirurgia de Cabeça ram analisadas, macroscopicamente e ultraestruturalmen- e Pescoço, Faculdade de Medicina de Ribeirão Preto, Universidade de São te.abertas O pavilhão a fim de auricular expor as apresenta estruturas forma da orelha, triangular as quais e côn fo- Paulo (USP), Av. Bandeirantes 3900, Ribeirão Preto, SP 14049-900, Brazil. 4 Departamento de Morfologia e Fisiologia Animal, Universidade Estadual cava com cristas irregulares e ápice pontiagudo; o conduto Paulista “Julio de Mesquita Filho” (Unesp), Campus de Jaboticabal, Via de auditivo externo é sinuoso em seu trajeto até a membrana Acesso Prof. Paulo Donato Castellane s/n, Jaboticabal, SP 14884-900, Brazil. timpânica; a bula timpânica encontra-se na parte poste- 583 584 Leandro L. Martins et al. rior-inferior do crânio; a orelha média é formada por uma tigate this animal as an experimental model for otologic região cavitária preenchida por estruturas ósseas e mem- research, focusing, on this occasion, on the description of branosas. É delimitada pela membrana timpânica e as jane- the macroscopic anatomy of the external and middle ear las redonda e oval, sendo a membrana timpânica de forma of the paca. plana e que veda todo o conduto auditivo. A anatomia da orelha da paca é semelhante à da cobaia e do ponto de vista MATERIALS AND METHODS de modelo experimental apresenta grandes vantagens em We used ten adult pacas culled for the selection and maintenance comparação com a orelha do rato. of equilibrium between males and females in the breeding stock TERMOS DE INDEXAÇÃO: Orelha, paca, Cuniculus paca, roedor, of the Sector of Wild Animals, Department of Zootechny, Faculty osso temporal, ultraestrutura. of Agrarian and Veterinary Sciences (FCAV), Jaboticabal Campus, Unesp, registered with the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA) as a breeding site for INTRODUCTION - There is an increasing search for appropriate experimen- tion no. 482508). tal models for the execution of otologic surgeries. Animal specimensThe animals of the were Brazilian euthanized fauna for with scientific an overdose purposes of midazolam (registra models are the most feasible alternative for otology rese- ((1mg/kg body weight) injected intramuscularly, plus a combina- arch, especially in surgeries that require microscopic en- tion of ketamine hydrochloride (20mg/kg body weight) and xyla- largement by involving delicate structures responsible for zine hydrochloride (1.5mg/kg) placed in the same syringe and injected intramuscularly. hearing such as the tympanic membrane and ossicular chain. Different experimental animal models are used such the temporal region of the skull was dissected in order to descri- as chinchillas, guinea pigs, rats, cats, dogs, and monkeys, be theAfter anatomical the verification region of and death, the insertionthe animal of was the decapitatedtympanic bulla. and among others (Browning & Granich 1978, Doyle & Rood The temporal bone was opened with a surgical clamp positioned 1980, Hellstrom et al. 1982, Giebink et al. 1985, Van der on the cervical spine up to the level of the tympanic bulla, which Ven et al. 1999, Piltcher et al. 2002). Each of these animal was located with the aid of the thumbs and then removed from species has advantages and disadvantages according to the the temporal bone. purposes of the study. To expose the cochlea, using the protocol of Albuquerque et Rats and guinea pigs are the animals most frequently al. (2009), we opened the bulla with the aid of a hemostatic clamp used in otologic research. According to Judkins & Li in the region of the posterior aerial sinus (mastoid) following its salience up to the petrous apex. The clamp was then positioned in the use of guinea pigs in this type of study has advantages the external auditory canal and the entire bony part was broken compared to rats. Also, some facility of handling and(1997), of ma- and raised. nipulation and dissection of the guinea pig’s cochlea has The study was approved by the Animal Ethics and Well-Being been observed. The bone fragility of the tympanic bulla of Committee (CEBEA) of FCAV, Jaboticabal Campus, Unesp (proto- the rat favors its opening for the exposure of structures of col no. 004734-09) according to the Ethical Principles of Animal the middle ear and cochlea, but also involves easy destruc- Experimentation adopted by the Brazilian College of Animal Ex- tion when the temporal bone is removed (Albuquerque et perimentation (COBEA). al. 2009). Guinea pigs and chinchillas are characterized as excel- RESULTS lent study models when topical drugs are applied to the In paca the auricle is a mobile cartilaginous structure con- middle ear. However, the cost for the acquisition and main- nected to the skull by skin, muscles and ligaments, with continuity through the external auditory canal up to the a fact that causes the use of this animal to be unviable. In contrast,tenance of guinea a sufficient pigs are number easy to ofmaintain chinchillas with is proper very high, care and hair. Because of its concave shape with irregular cristae as recommended by the guidelines for the care and use of andtympanic a pointed membrane. apex, it presentsIts surface several is covered regions with with fine salient skin laboratory animals of the Institute of Laboratory Animal delimitations (Fig.1A,B). The auricle measures approxi- Resources, Comission on Life Sciences, National Research mately 4.5cm from base to apex. Council, National Academy Press, Washington, DC., 1996 The temporal bone is located in the posteorinferior re- (Wysocki 2005). gion of the skull between the occipital bone caudally, the Swine and dogs are considered to be excellent models parietal bone dorsally and the frontal, palatine, sphenoid, for otology experimentation but they require elaborate fa- maxillary end ethmoid bone rostrally. The tympanic bulla is cilities with high maintenance costs (Damatta 2010). located in the posteroinferior part of the skull (Fig.2). Squa- Representing an alternative as experimental animals, mous bone forms a process that joins a discrete zygomatic the pacas, which are rodents, can become a good option for arch cranially fused with maxillary bone. It can be seen that research purposes. The largest rodent in the Brazilian fau- this bone structure presents a region with an ivory-like as- na (Matamoros 1982), the paca reaches 80 cm in body leng- pect, with rugosities and areas of bone aeration (Fig.3A,B). th and 12 kg in weight (Pachaly et al.